Hello Tina,
It sounds like your DVD Drive is not recognizing discs in the drive. Try using [guide|4491|this guide] to manually clean the lens, or replace as necessary. If you do not feel you are up to lens replacement you can try [guide|5164|replacing the drive] wholesale.
Be aware that if your Wii has been under heavy use (such as moving it frequently) your solution could be as easy as a loose cable from the motherboard to the DVD drive. Refer to [guide|3460|this guide] to make sure all your cables are solidly seated.
Hope this helps.